Ocular Pharmacology

Question 1

What are the 3 ways a drugs is administered topically is distributed in the eye?

Answer 1

• Drained by lacrimal drainage
• Penetrates the cornea/sclera
• Enters systemic circulation through conjunctival and nasal mucosa vessels

Question 2

What % of the tear film is turned over every minute?

Answer 2

15%

Question 3

What are the advantages of topical administration into the eye?

Answer 3

• Convenient
• Easy
• Specific
• Minimal side effects

Question 4

What needs to be considered when topically administering a drug into the eye?

Answer 4

Intraocular bioavailability is relatively poor - 1-10% of instilled drug reaches the anterior chamber
Palpebral fissure can only hold about 20μL – dropper bottle delivers 50μL/drop

Question 5

How can intraocular bioavailability be improved?

Answer 5

• Increasing retention time on ocular surface

- Optimising the ability of the drug to penetrate the cornea

Question 6

What are the different formulas a drug can come in for ocular treatment?

Answer 6

• solution
• suspension
• ointment
• viscous gel
• solid delivery
• sub-conjunctival injection

Question 7

Most preparations are formulated to enter the eye through which part?

Answer 7

Cornea

Question 8

How do drugs move through the epithelium layer of the cornea?

Answer 8

Paracellularly - between cells (water soluble)

Transcellular - through cells (lipid soluble)

Question 9

The stroma of the cornea facilitates the diffusion of which drug types?

Answer 9

Water soluble

Question 10

Which layer of the cornea can both lipid and water soluble drugs pass through with ease?

Answer 10

Endothelium

Question 11

To be able to penetrate the cornea a drug should have what characteristic?

Answer 11

Hydrophilic and lipophilic

Question 12

Are ionised forms water or lipid soluble?

Answer 12

Water soluble
(unionised are lipid soluble)

Question 13

Do ionised or unionised forms cross the corneal epithelium more easily?

Answer 13

Unionised

Question 14

Once in the stroma what happens to the unionised drug?

Answer 14

It becomes ionised because of its relative abundance, which facilitates its movement across the stroma

Question 15

Which action of a drug can render it unavailable?

Answer 15

Binding to the tear film

Question 16

How do large hydrophilic molecules enter the eyeball?

Answer 16

Absorption across the conjunctiva and sclera

Question 17

Once a drug penetrates the cornea where does it move into?

Answer 17

Aqueous humour, iris and ciliary body

Question 18

If a drug is administered via a non-corneal route where are its levels highest?

Answer 18

Anterior uvea

Question 19

How do the levels of being lipophilic change for a drug treating more superficially e.g. cornea vs deeper structures e.g. anterior uvea

Answer 19

Superficial = less lipophilic
Deeper = more lipophilic

Question 20

The Blood:ocular barrier consists of?

Answer 20

The blood:aqueous and the blood:retinal barriers

Question 21

Why can agents cross more easily into the anterior segment than the posterior?

Answer 21

The blood:aqueous barrier is leakier than the blood:ocular barrier so systemic agents can cross more easily into anterior segment

Question 22

Give some examples of when we would want to change the pupil size

Answer 22

• Dilate the pupil to enable fundic examination
• Relax ciliary body to relieve spasm
• Constrict pupil to open drainage angle

Question 23

What is the proper word for dilation of the pupil?

Answer 23

Mydriasis

Question 24

What is the proper word for relaxation of the ciliary body?

Answer 24

Cycloplegia

Question 25

What is the proper word for constriction of the pupil?

Answer 25

Miosis

Question 26

Which 3 drugs can be used for mydriasis?

Answer 26

Atropine
Tropicamide
Phenylephrine

Question 27

Give some tear substitute examples

Answer 27

• Ciclosporin ointment
• Pilocarpine
• Aqueous substitutes
• Mucin replacements
• Lipid replacements

Question 28

What is glaucoma?

Answer 28

Sustained increased intraocular pressure, causes pain, blindness and irreversible changes in eye structure

Question 29

What is the cause of glaucoma and how can it be treated?

Answer 29

• Recued aqueous humour outflow

- Need to either increase outflow of aqueous humour or reduce its production

Question 30

In an acute presentation of glaucoma what is used as a first line treatement?

Answer 30

Osmotic diuretics

Question 31

How do carbonic anhydrase inhibitors treat glaucoma?

Answer 31

Inhibit that action of carbonic anhydrase which catalyses the reaction to form bicarbonate ions which draws water into the aqueous humour - this is inhibited